Combining ability and heterotic grouping of highland transition maize inbred lines

The objectives of the present study were to examine combining ability of highland transition maize inbred lines for grain yield and other desirable traits, to determine heterotic groups of germplasm of the inbred lines and to identify promising hybrid crosses. Twenty-six inbred lines were factorially mated (Design II) with six testers and the resulting F1s along with two checks and the parents were evaluated in separate trials at five locations namely: Ambo, Awassa, Bako, Holeta and Kulumsa, all in Ethiopia during 2002. General combining ability (GCA) and specific combining ability (SCA) effects were calculated using line x tester analysis. GCA mean squares due to lines and, testers were highly significant (P < 0.01) for all the traits. Similarly SCA mean squares for most traits except for days to physiological maturity and for northern leaf blight (NLB, caused by Exserohilum turcicum) were found highly significant (P < 0.001). The ratio of GCA/SCA mean square further exhibited the preponderance of additive gene effects in the inheritance of all traits. Estimates of GCA effects indicated that three inbred lines showed good combiners for grain yield. For days to silking four, for grey leaf spot (GLS caused by Cercospora zeae-maydis Tehon), three, and for NLB one inbred lines revealed significantly negative GCA effects. These inbred lines can be a good source of variability for the improvement of the traits in the breeding program. Significantly different SCA effects were revealed for crosses involving most traits. A number of single crosses out-yielded the hybrid checks (BH660 and BH 540) and also revealed desirable plant height performances. Moreover, two best contrasting heterotic group (Pool 9A-MHM x 142-1-e) composed of 13 and 10 inbred lines, respectively, have been determined to initiate heterotic source germplasm. This heterotic group may have wide applicability in the east African highland maize breeding programs, as well

Relationship between hybrid performance and AFLP based genetic distance in highland maize inbred lines

The objectives of this study were to determine the crossing performance of highland maize inbred lines for grain yield, days to silk and plant height; estimate genetic distance (GD) among the inbred lines and in association with tester parents, and to investigate the relationship of GD with hybrid performance and midparent heterosis (MPH). A total of 26 inbred lines were crossed with six (population and line) testers in a factorial-mating scheme. The F1’s and the parents were evaluated at five locations in Ethiopia. Nine amplified fragment length polymorphism (AFLP) primer pairs were used to genotype all the parents. The F1’s were found to vary widely for grain yield and other traits measured. Yield superiority of more than 30% over the best hybrid check was obtained for some testcross hybrids. Midparent heterosis on average was moderate for grain yield and, plant height. And for days to silking, MPH values were mostly negative. Mean GD values determined from the inbred lines by population tester (0.680) and line tester (0.661) combinations were not significantly different. Cluster analysis separated the tester parents from the corresponding inbred lines. AFLP grouping of the inbred lines was in agreement with their pedigree records. Genetic distances derived from the inbred lines × all testers and from the population testers’ sub-group were not positively correlated with hybrid performance and MPH for most traits. In contrast, correlations of GDs involving the line testers’ sub-group with F1’s and MPH were significantly positive but with low magnitude to be of predictive value